Bleaching clay



Fli- 8309 unlluw w Patented Jan. 18, 1944 cause mil" minim.

\JUul Ul E BLEACHING CLAY Ira Williams, Burger, Tex., assignortoS'godaCorporation, Huber, Ga., a corporation of New Jersey No Drawing.Application MarchZll, 1941,. Serial No. 384,288

12 Claims.

This invention relates to thebleachingoi clay and particularly to a.method. of bleaching clay whereby the brightness of the clay isimproved.

It is common practice to treat clays, especially those which are to beemployed in the manufacture of. paper, in a manner. which will improvetheir color. Since the color of clay is usually due to the presence ofoxides of iron. in an insoluble form, these treatments usually have,been directed-toward reducing the-oXides-of iron to-sol uble ferrouscompounds which could be brought intosolution and thus removed from theclay. Various compounds of hydrosulfurous acidhave been employed forthis purpose, such as, for example, the sodium, zinc and calciumhydrosulfites. These hydrosulfites usually have been added directly tothe clay in' the form of a slip or, in some cases, have been formed insitu in the clay slip by the interaction of'a metallic powder,

suchas' Zinc'dust', with sulfurous acid or its salts. Frequently, strongnon-oxidizing mineral acids have been added in order to assist thesolution of the reduced iron compounds.

In the preparation ofclay, particularly for use in the manufacture ofpaper and for usein'coating compositions, it is usual. to employ both adegritting and a bleaching operation. A typical example of such aprocess comprises suspending clay in Water to produce a clay slipcontaining from about to about of clay and treating such clay slip witha peptizing agent, such as sodium pyrophosphatezor ammonia, inordertogreatly reduce the viscosity of the slip. The coarse material,consisting largely of sand, mica and clay particles, is'permitted'tosettle and the Hydrosulfurcus acid and its compounds-are relativelyunstable and rapidly decompose in solution, particularly at elevated.temperatures andespecially in the presence of strong mineral acids.hydrosulfurous acid, such. as sodium hydrosulfite. not attempted toemploy the hyclrosulfuro-us compoundsfor the bleaching ofclay atelevated temperatures, as it was expected that the hydrosulfurouscompounds would: largely decompose undersuch-conditions whereby largepropor tionsof. the hydrosulfurous compound would be wasted; and-poorer.results would be obtained;

This is particularly true of the salts of' Accordingly, those skilled inthe art have- It is'an object of my invention to providev an improvedmethod for bleaching argilaceous materials. Another object is to providea method of bleaching clay in a greatly reduced time. A further objectis to provide a method of bleaching clay in a reduced length of timeand, at the same time, increasing the effectiveness of the bleachingmaterials and securing an improvement in the color ofclay beyond thatusually employed with such bleaching materials. Other objects are toadvance theart. Still other objects will, appear hereinafter.

The above-and other objects may be accom plished in. accordance with myinvention which comprises bleaching clay slips by means of Water solublehydrosulfurous compounds at tempera-. tures between 50 C. and 100 C;,either with or without an added strong. non-oxidizing mineral acid. Ihave, found that, in spite of the reducedstability of thehydrosulfurous' compounds at such elevated temperatures, by employingsuch compounds at such temperatures, I am able to greatly reduce thetime required for bleaching the clay and, at thesametime, obtainanincreased degree of bleach and a clay of increased brightness. Whilevmaterially improved results are-obtained by employing temperaturesbetween 50 and 100- 0;, I'have found that the best results are obtainedat temperatures of from about C. to about C. and I, therefore, preferthe latter temperatures.

By the terma hydrosulfurous compound, I mean to include hydrosulfurousacid, salts of hydrosulfurous acid and the correspondingsulfoxylates. Bythe terms an alkali metal hydrosulfurous compound and a zinchydrosulfurous compound,' I' mean the alkali metal and zinc salts;respectively, of hydrosulfurous acid and the sulfoxylates. Of thehydrosulfurous compounds, which maybe employed in accordance with myinvention, it will generally be preferred to employ the metal salts, andparticularly the Zinc, alkali metal and alkaline earth metal salts. Bythe term sulfoxylate, I mean the compounds formed by the reaction ofaldehydes with metal" salts ofhydrosulfurous acid. Of'these, theformaldehyde sulfoxylates, obtained from formaldehyde and salts ofhydrosulfurous acid, will be preferred. Thespecific compounds, which Iparticularlyprefer to employ in accordancewith my invention are, sodiumhydrosulfite, zinc hydroe sulfite, calcium hydrosulfite and thecorrespond.- ing-salts of formaldehyde sulfoxylate, particularly sodiumformaldehyde sulfoxylate.

The amount of hydrosulfurous compound, which will be employed inaccordance with my invention, will vary largely with the particularclay, particularly its color, and with the amount of bleaching desired;Generally, from about 0.05 to' about 0.252% of hydrosulf urous compoundbased on the clay will be satisfactory for most clays and most purposes.This amounts to from about 1 to about 5 pounds of hydrosulfurouscompound per ton of clay. Larger amounts of hydrosulfurous compound maybe employed, if desired, but are generally unnecessary and uneconomical.I preferably employ from about 0.1 to about 0.2% of hydrosulfurouscompound based on the clay.

It is possible, at the elevated temperatures employed in accordance withmy invention, to bleach clay in the absence of added strong mineralacid. However, under such circumstances, the bleaching is lesssatisfactory than in the presence of acid and the color is more likelyto reappear on drying the clay. The reason for this is that acid assistsin causin solution of the iron and hence results in a more completeremoval of the iron compounds from the clay. Acidic materials, which maybe employed with the hydrosulfurous compounds in the process of myinvention, are the strong non-oxidizing mineral acids, such as sulfuricacid, hydrochloric acid, phosphoric acid. sulfurous acid and the likeand acidifying com pounds of such acids which release such acids insolution to produce acidic solutions. When a strong mineral acid isemployed with the hydrosulfurous compounds of my process, such acid maybe added to the clay slip prior to the addition of the hydrosulfurouscompound, with the hydrosulfurous compound, or even after the bleachinghas been completed but prior to separation of the clayfrom theslip as byfiltration.

The hydrosulfurous compounds may be added to the clay slip in dry form.However, it will generally be preferred to add such compounds in theform of aqueous solutions thereof. In some cases, it will be preferredto form the hydrosulfurous compounds in situ in the aqueous claysuspension as by treatin the Clay slip with sulfur dioxide, sodiumbisulfite and the like and with a metal powder, such as zinc dust. Whenthe hydrosulfurous compound is formed in situ, it will generally bepreferred to have a strong mineral acid present so as to facilitate theproduction of the hydrosulfurous compound.

In order to illustrate my invention more clearly, the preferred modes ofcarrying the same into effect and the advantageous results to beobtained thereby, the fOllOWing examples are given:

Example 1 A 35% aqueous suspension of degritted Georgia Kaolin wastreated with three pounds of sodium hydrosulfite and four pounds ofsulfuric acid per ton of clay. Portions were bleached at differenttemperatures for sufiicient time to produce the maximum bleachingefiect. The clay was then recovered, dried and the brightnessdetermined. The brightness of the unbleached clay, when washed withsulfuric acid alone, was 82.31. The following are the results obtainedwith the bleached samples:

Temperature of bleach, C. Time of bleach Brightness -The improvement of0.9 point in brightness, between the sample bleached at 32 and that lokached at 80, is readily apparent to the unaided eye and constitutes animportant increase in brightness.

Example 2 A 35% aqueous suspension of degritted clay was acidified with5 pounds of aluminum sulfate per ton of clay and was then treated withzinc hydrosulfite at the rate of 2.5 pounds per ton. When bleached for 2/2 hours at 30 C., a brightness of 81.50 was obtained. When bleached for20 minutes at C., a brightness of 82.22 was obtained.

Example 3 A 40% aqueous suspension of degritted clay was treated with3.75 pounds of sulfuric acid and 0.66 pound of zinc powder per ton ofclay. One portion was treated with an aqueous solution of sulfur dioxideequivalent to one pound per ton of clay. After bleaching for 2 hours at30 0., the brightness was 83.13. The second portion was heated to 80 C.and sulfur dioxide, equivalent to one pound per ton of clay, wasintroduced slowly and with stirring into the bottom of the clay slip.Some of the sulfur dioxide escaped due to the decreased solubility atthe elevated temperature. The slip was bleached for 20 minutes and theclay recovered by filtration. The brightness was 83.96.

Example 4 A clay slip was treated with two pounds of zinc powder and 5.5pounds of sodium bisulfite per ton of clay and divided into twoportions. One portion was acidified with ten pounds of sulfuric acid perton of clay and bleached for /2 hour at 25 C. The brightness was 83.98.The second portion was heated in a closed container to 80 C. andacidified with ten pounds of sulfuric acid per ton of clay. After 20minutes, the brightness was 84.20.

Example 5 A clay slip, containing 42 percent of degritted kaolin, wasprepared and portions were treated with 2.5 pounds of sodiumformaldehyde sulfoxylate and five pounds of acidifying ingredient perton of clay. The portions were bleached under various conditions of timeand temperature and the brightness determined. The results are shown inthe following table:

Temper- Time of Acidifymg ingredient ature of bleach in Brightnessbleach, C. minutes Sulfuric acid 25 120 82.88 Do 60 30 83. 52 80 20 83.58 20 83. 12 25 150 82. 81 80 15 83. 80 80 35 83. 70 95 60 83. 34 25 15081. 70 8O 20 83. 52 30 82. 54 80 2O 83. 58

The above examples are given for illustrative purposes only and myinvention is not to be limited to the specific embodimens disclosedtherein. It will be readily apparent to those skilled in the art thatmany variations and modifications may be made therein, particularly inthe specific agents employed and their proportions. The concentration ofclay in the slip may be varied within wide limits and the bleachingprocess may be carried out without subjecting the clay to a degrittingstep. Ac-

iiilit'maalaiMom CATION F TEXTILES & HBE-RS, 2,339,594 3 1 1 0cordingly, I intend to claim my invention broad= ly as in the appendedclaims.

From the above description, and particularly the examples given therein,it will be apparent that, while others have considered it impracticableto employ hydrosulfurous compounds for the bleaching "6T clay at theelevated temperatures employed by me, I have been able, by the use ofsuch higher temperatures, to greatly reduce the time required forbleaching the clay and, at the same time, have been able to obtain amore efficient bleaching action and clay of a brightness greatlysuperior to that which it was possible to obtain by the processesheretofore employed. These results were unobvious and could not havebeen predicted.

I claim:

1. The process which comprises bleaching a clay slip under acidicconditions by means of a water-soluble hydrosuliurous compound at temperatures between 50 C. and 100 C. and in a proportion of from about0.05% to about 0.25% based on the clay.

2. The process which comprises bleaching a clay slip under acidicconditions by means of an alkali metal hydrosulfurous compound attemperatures between 50 C. and 100 C. and in a proportion of from about0.05% to about 0.25% based on the clay.

3. The process which comprises bleaching a clay slip under acidicconditions by means of a water-soluble metal salt of hydrosulfurous acidat temperatures between 50 C. and 100 C. and in a proportion of fromabout 0.05% to about 0.25% based on the clay.

4. The process which comprises bleaching a clay slip under acidicconditions by means of a zinc hydrosulfurous compound at temperaturesbetween 50 C. and 100 C. and in a proportion of from about 0.05% toabout 0.25% based on the clay.

5. The process which comprises bleaching a clay slip under acidicconditions by means of an'alkali metal hydrosulfite at temperatures offrom about 65 C. to about 85 C. and in a proportion of from about 0.1%to about 0.2% based on the clay.

6. The process which comprises bleaching a clay slip underacidicconditions by means of g, sodium hydrosulfite at temperatures of fromabout 65 C. to about 85 C. and in a proportion of from about 0.1% toabout 0.2% based on the clay.

7. The process which comprises bleaching a clay slip under acidicconditions by means of a water-soluble metal salt of a sulfoxylate attemperatures of from about 65 C. to about 85 C. and in a proportion offrom about 0.1% to about 0.2% based on the clay.

8. The process which comprises bleaching a clay slip under acidicconditions by means of an alkali metal salt of a sulfoxylate attemperatures of from about 65 C. to about 85 C. and in a proportion offrom about 0.1% to about 0.2% so based on the clay.

9. The process which comprises bleaching a clay slip under acidicconditions by means of an alkali metal salt of formaldehyde sulfoxylateat temperatures of from about 65 C. to about 33, 85 C. and in aproportion of from about 0.1%

to about 0.2% based on the clay.

10. The process which comprises bleaching a clay slip under acidicconditions by means of the sodium salt of a sulfoxylate at temperaturesso of from about 65 C. to about 85 C. and in a proportion of from about0.1% to about 0.2%

based on the clay.

11. The process which comprises bleaching a clay slip under acidicconditions by means of sodium formaldehyde sulfoxylate at temperaturesof from about 65 C. to about 85 C. and in a proportion of from about0.1% to about 0.2% based on the clay.

12. The process which comprises bleaching a 40 clay slip under acidicconditions by means of zinc hydrosulfite at temperatures of from aboutC. to about C. and in a proportion of from about 0.1% to about 0.2%based on the clay.

IRA WILLIAMS.

